3/10*(2х+3.9/10)=1.4/5:1.7/533/10*2х+3/10*9/10=9/4:60/53
3/5х+1.17/100=1.59/100
3/5х=1.59/100-1.17/100
3/5х=42/100=21/50
х=21/50:3/5
х=21/50*5/3
х=7/10
проверяем
3/10*(2*7/10+3.9/10)=1.4/5:1.7/53
1.59/100=1.59/100
3/10*(2х+3.9/10)=1.4/5:1.7/53
3/10*2х+3/10*9/10=9/4:60/53
3/5х+1.17/100=1.59/100
3/5х=1.59/100-1.17/100
3/5х=42/100=21/50
х=21/50:3/5
х=21/50*5/3
х=7/10
проверяем
3/10*(2*7/10+3.9/10)=1.4/5:1.7/53
1.59/100=1.59/100